This invention relates generally to fuel flow systems for an internal combustion engine, and more particularly to apparatus and method for testing the flow of fuel from the fuel tank to such an engine.
In older conventional fuel systems, fuel is pumped at a relatively high rate (e.g., 0.4–0.5 gpm) from the fuel tank to the engine which uses only a relatively small amount of the fuel, the remaining unused portion being delivered back to the fuel tank for recycling. This type of system is often referred to as a standard return fuel system, since the unused fuel is returned to the fuel tank. One drawback of a “return” system is that the temperature of the fuel rises over time as it cycles past the engine and returns to the tank, and the increase in temperature leads to the evaporation of greater amounts of fuel into the atmosphere.
In more recent fuel systems, fuel is pumped at a much lower rate (e.g., 0.05–0.1 gpm) corresponding to the actual need of the engine. All of the fuel pumped to the engine is used; none is returned to the fuel tank. This type of system is known as a “returnless” fuel system.
In testing for proper fuel flow to an engine, it is important to test both the rate of fuel flow and fuel pressure, since testing only one of the conditions is often not sufficient for reliably and accurately diagnosing a problem with the fuel system (e.g., bad fuel pump, faulty pressure regulator, clogged fuel filter, blocked fuel lines, etc.). In a “return” system, the testing for both conditions is relatively easy, since the flow rates are relatively large. However, in a “returnless” system, the flow rate is difficult to measure accurately. This can cause the misdiagnosis of a problem with the fuel system. As a result, costly components, such as fuel pumps, are unnecessarily replaced in a vain attempt to correct a problem arising from a different source.
There is a need, therefore, for an improved apparatus and method for reliably and accurately testing both return and returnless fuel systems.